The present invention relates to a droplet discharge head which circulates a recording liquid in a pressure chamber, and discharges droplets of the recording liquid from a nozzle hole, and an image-forming apparatus equipped with the droplet discharge head.
Generally, an image-forming apparatus such as a printer, a fax machine, a copier, or a multifunction peripheral thereof is equipped with a droplet discharge head for ink-jet recording, or the like. A droplet discharge head performs recording by discharging a recording liquid (ink) toward sheets of paper (which are not limited to paper, but include OHP (overhead projector) sheets, or the like) from a nozzle hole thereof. By using such a droplet discharge head, it is possible to record a high-definition color image at high speed.
The droplet discharge head generally has a plurality of nozzle arrays, and a plurality of pressure chambers corresponding to the nozzle arrays. Generally, the pressure chambers communicate with a common recording liquid storage (common supply passage) which has a comparatively large capacity.
By selectively applying energy to the pressure chambers, the recording liquid is discharged from nozzle holes, and an arbitrary image is obtained on demand. As an energy-applying medium, a piezoelectric element and a heater are used.
In recent years, output of higher-quality images at higher speed has been requested. In order to realize higher-quality images, the number of nozzles and nozzle density have increased. This has resulted in each interval between the pressure chambers becoming narrower. Additionally, the frequency of applied energy tends to be higher. On the other hand, in order to provide higher speed output, lengthening of the head has been proposed, and in recent years, a so-called line-type printer which covers an entire width range of the recording medium has become common.
Additionally, such a droplet discharge technique is widely applied to not only image formation, but also to so-called three-dimensional shaping systems and bioscience fields, such as tissue engineering, or the like, and is used for the purpose of discharge of not only ink, but also various recording liquids.
In addition, a droplet discharge head is known which circulates a recording liquid (ink) in a pressure chamber, generates pressure in the pressure chamber by a piezoelectric element, and discharges the recording liquid in the pressure chamber from a nozzle hole. The droplet discharge head has a common supply passage and a common return passage on an upstream side and a downstream side of the pressure chamber, along a circulation direction of the recording liquid, and circulates the recording liquid in the pressure chamber by generating a difference in pressure between the common supply passage and the common return passage (see Japanese Patent No. 4617798, and Japanese Patent No. 3097718). In such a droplet discharge head, the recording liquid in the pressure chamber always flows, and therefore, it is possible to prevent materials included in the recording liquid from being deposited.
Furthermore, as an energy-generating element, although it is an example of a droplet discharge head using a heating resistor, on a side close to an upstream side of a pressure chamber along a circulation direction of a recording liquid, a structure in which a circulation passage on an upstream side and a circulation passage on a downstream side communicate with an ink reservoir layer is disclosed (see Japanese Patent Application Publication No. 2002-254643).
In Japanese Patent Application Publication No. 2002-254643, the circulation passages are formed inside of a supporting plate, and a passage-forming base plate is formed of an alumina-glazed base plate, a single crystal silicon, metal, or the like by a photolithography method, and therefore, it is possible to perform micro-fabrication.